There has been conventionally known a grain huller including a pair of rolls that are disposed so as to be brought into pressure contact with each other, a grain tank and a hopper that are disposed above the pair of rolls. In this grain huller, grain contained in the grain tank is supplied to a portion between the pair of rolls by way of the hopper, and the pair of rolls rotate to remove chaff of the grain that is sandwiched between the pair of rotating rolls.
In such a grain huller, repetition of hulling operation causes abrasion of surfaces (such as rubber surfaces) of the pair of rolls so that outer diameters thereof decrease, which results in decrease of the pressure contact force between the pair of rolls.
In view of the above problem, there has been known a configuration in which one of a pair of roll shafts for respectively supporting the pair of rolls is made movable and this position-movable shaft is moved so as to adjust the distance between the axes of the pair of roll shafts (see, for example, Patent Document 1 that is mentioned below).
However, in the case where the position of the position-movable shaft is adjusted in accordance with degrees of abrasion of the pair of rolls, also displaced is the position of contact between the pair of rolls. In this case, the position of grain to be supplied from the grain tank by way of the hopper is displaced from the position of contact between the pair of rolls, resulting in deterioration in efficiency of hulling operation.
In order to solve this problem, there has been proposed the following configuration.
For excellent hulling outcome, it is important to supply, uniformly and regularly as much as possible, grain from the hopper to the portion between the pair of rolls. In other words, what is important is to supply grain, which has flown downward through the hopper, precisely to the position of contact between the pair of rolls.
For example, Patent Document 1 proposes a configuration in which a supply plate is provided between the hopper and the pair of rolls and the position of the supply plate is manually adjustable so as to direct a distal end of the supply plate to the position of contact between the pair of rolls.
In the grain huller described in Patent Document 1, adjustment of the position of the supply plate in accordance with degrees of abrasion of the pair of rolls makes it possible to supply grain from the grain tank by way of the hopper precisely to the position of contact between the pair of rolls. However, in this grain huller, the position of the supply plate needs to be manually adjusted, which requires troublesome work for positional adjustment of the supply plate. In addition, the grain huller of Patent Document 2 needs to stop hulling operation during the positional adjustment of the supply plate, which causes deterioration in efficiency of hulling operation.
To the contrary, Patent Document 2, which is mentioned below, discloses a configuration in which the position of the supply plate disposed between the hopper and the pair of rolls is automatically adjustable.
More specifically, the grain huller described in Patent Document 2 includes a sensor that electrically detects the outer diameter of one of the pair of rolls, and the position (slant angle) of the supply plate is controlled in accordance with the diameter of the roll to be detected by the sensor.
While being free from the above problems arising in the grain huller of Patent Document 1, the grain huller described in Patent Document 2 requires the sensor as well as a controller for controlling the position of the supply plate based on an electrical signal transmitted from the sensor, resulting in increase of the number of components and complexity in configuration of the apparatus.
Moreover, in the configuration described in Patent Document 2, in a case where deterioration or the like due to repeated use causes undulation of the outer surfaces of the pair of rolls, the sensor erroneously detects the size of the undulated shape as the outer diameter of the roll, which may result in failure in stable control of the position of the supply plate.
[Prior Document 1]
    Japanese Patent Application Laid-open No. S56-28601[Prior Document 2]    Japanese Patent Application Laid-open No. H9-313959